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These are the auxiliary air inlets for the ECS (Environmental Control System): (image source) They provide air to the primary heat exchanger (A18), which is then exhausted via the ram air exhaust (A20, the tubes visible behind the inlets in your picture).


It's called 'toe-in' and it's done basically to match the local airflow which is slightly divergent (heading outboard along the underside of the wing). If the engines were mounted exactly parallel to the fuselage, they would be moving slightly obliquely through the local airflow and therefore incurring extra unnecessary drag. Another view of a 777 showing ...


Air density or pressure altitude must be factored in when comparing engine thrust figures. At cruise, FL400, air density will be about one fifth. Max thrust (or max HP for piston engines) will also be one fifth, as will air resistance/parasite drag. Air mass flow will be one fifth, so will fuel flow/burn. Even lift will be one fifth for a given air speed ...

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